InfoPath Dev

I have been tasked with creating a form for users to book onto a course. The course is limited to 30 people. I need this information to be displayed on the form and count down each time someone books onto the course. Once all 30 places are taken, users are then unable to book onto the course.

 The course is ran twice a week and so users should be able to select the course they want to go on.

Is this possible? If so how do i add the above abilities.

 Im new to infopath however any help regardless of how detailed would be much appreciated.

Your repeating group will need a field that marks each course as booked. And then for the validation check, you would want to count the number of rows in your repeating group where the course is booked; and if it reaches 30, don't allow adding more.

I attached a sample form with the basic proof of concept - hope it helps.